<!DOCTYPE html>
<html lang='en'>

<head>
  <meta charset='UTF-8'>
  <meta http-equiv='X-UA-Compatible' content='IE=edge'>
  <meta name='viewport' content='width=device-width, initial-scale=1.0'>
  <title>Document</title>
  <script src='https://cdn.jsdelivr.net/npm/vue/dist/vue.js'></script>
</head>

<body>
  <div id='app'>
    <!-- <input type="text" v-model="message"> -->
    <input type="text" :value="message" @input="inputValue($event.target.value)">
    <h2>message:{{message}}</h2>
  </div>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        message: 'hello world'
      },
      methods: {
        inputValue(value) {
          this.message = value
        }
      }
    })
  </script>
</body>

</html>